Remove the HostDict class, as it is not used anymore.
Fix for regression: docker_hosts group is always empty (null)

The base_url key was moved into the server dict in the host dict.
The docker_hosts group consists of all the base_url strings in all server dicts in all host dicts in the hosts list.
Also, all base_url strings need to be included only once.
Documentation update: updated the requirement to docker-py >= 0.6.0

The script uses the docker.utils.kwargs_from_env function to parse environment variebles for the connection kwargs.
The function is available from docker-py 0.6.0 up.
Added description of the DOCKER_TLS_VERIFY and DOCKER_CERT_PATH environment cariables to the comments.
Followed documetation changes in docker.py:

- dockerp-py >= 0.6.0 requirement
- new environment variables: DOCKER_TLS_VERIFY, DOCKER_CERT_PATH
Added new example configuration to docker.yml.
Fix for old server configuration import not working properly (as in "at all").
Make it possible ot explicitly disable tls connection to a Docker host.

Make it possible ot explicitly disable tls connection to a Docker host, no matter what the environment or the default settings are.
Added an example to the docker.yml file.
Make sure no tls_config is imported for old-style configurations.